Experimental investigation on properties of recycled aggregate concrete with optimized Ball Milling Method

Numerous research studies were conducted to improve the weak properties of recycled aggregate as a construction material during the last two decades. Most of these studies mainly focused on minimizing the undesired characteristics of the recycled aggregate through various treatment techniques to strengthen the attached old mortar or remove it from the recycled aggregate. Mechanical Treatment Methods (MTMs) used to remove the attached mortar from the aggregates were evolved over the years. Among available methods of treatments in the literature, the number of studies investigated the MTMs with an optimization process is limited. In lack of proper optimization process with rubble quality identification, mechanical treatment methods may be ineffective to provide concretes with sufficient properties, and they may yield to extra energy consumption and carbon emission. In other words, the optimization of treatment methods and determination rubble quality are two essential steps for having satisfactory results on the recycled aggregate. In this study, an optimization process is applied using the Los Angles test machine through the conducted Ball Milling Method (BMM). During the BMM process, various combinations of rotation (R) (100-200-300-400-500) and the steel ball (S) (0-2-5-7-10-12) applied to the recycled aggregate. Analysis results demonstrated the effectiveness of reducing the 8.95% water absorption value of the untreated recycled aggregate to 0.84% after the optimization process of BMM. Then, seven concrete specimens including 0-20-40-60% recycled aggregate (RA) and improved recycled aggregate (RA-i) mixes produced in the framework of the experimental study. For comparison purposes, engineering properties of 28 days concrete are determined. The use of RA-i up to 60% in concrete has not influenced the physical and mechanical properties, distinctively. After the optimization process, the RA use in concrete increased up to 60% which is twofold of the optimum RA value in the literature. As a result, optimized BMM improved the mechanical and physical characteristics of RA and increased the use of RA ratio in concrete mixes without any trade-off. (C) 2019 Elsevier Ltd. All rights reserved.